MICROGRAVITY SURVY FOR OUTLINING WEAKNESS AND CAVITY AREAS IN KIRKUK SILO

Abstract

According to an agreement form between Iraqi Grains Company / Kirkuk Branch and GEOSURV, a microgravity survey was conducted in Kirkuk Silo, 12 km southwest Kirkuk City. The aim of the survey is to outline positions and subsurface extensions of weakness zones, which are affected by the near-surface activity of groundwater. A total of 1171 gravity point were measured. The points are distributed on 67 gravity profiles ranging in length between 90m to 320m with a 5m spacing interval between two adjacent points. The results were displayed as Bouguer anomaly, regional and residual maps and profiles that showed the distribution of negative anomalies, which are related to subsurface weakness zones. The depths of sources of these anomalies were estimated by using 2D forward modelling and power spectrum method that showed three depth levels; 2.16m, 5-6m, which shows a main effect and 12m. Moreover, the near-surface groundwater movement and directions map was prepared according to the distribution of the negative anomalies and the general trend of the slope direction in the study area. The study recommends the delineated subsurface weakness zones for cement grouting, however, putting steel sheets around the studied sites in order to stop near-surface groundwater drainage is highly recommended before beginning the grouting.